An arrangement of the kind illustrated in FIG. 25 by way of example is known as an electroluminescent storage device (refer to the specification of Japanese Patent Kokai Publication No. JP-A-2-14868 pages 5 and 6, FIG. 2). As shown in FIG. 25, this conventional electroluminescent device includes an electroluminescent element 40; a plurality of memory cells 22 corresponding to the electroluminescent element 40; a current source 28 (a current mirror comprising transistors 26 and 27); current control means (transistors) 24, which correspond to the plurality of memory cells 22, connected to corresponding ones of the memory cells 22 and responsive to signals, which are held in the memory cells 22, for controlling current that flows from the current source 28 to the electroluminescent element 40; and control logic, a column data register, display input/readout logic and row strobe register, etc., none of which are shown, for supplying the memory cells 22 with signals Bn to B0 representing luminance required by the electroluminescent element 40.
Current corresponding to the signals held in the memory cells 22 flows through transistors 24n to 24n-3, current that is the sum of the currents that flow through the transistors 24n to 24n-3 enters the drain of the transistor 26 constituting the input end of the current source (current mirror) 28, and the mirror current of the input current is output from the drain of the transistor 27, which constitutes the output end of the current source (current mirror), and is supplied to the electroluminescent element 40.
In the arrangement shown in FIG. 25, the relationship between the input data signal and the output current (and therefore luminance) is a positive proportional relationship (gamma value=1.0). Consequently, in order to perform a correction such as one where the gamma value is 2.2, the gamma correction must be applied to the video signal stored in the memory cells 22. Since the human eye is sensitive to dark colors, an image will appear more natural if the luminance of the input signal satisfies a luminance=(signal strength) (e.g., γ=1.8, 2.2, etc.) relationship rather than a positive proportional relationship. In general, therefore, the relationship between panel luminance and the video signal is provided with a gamma characteristic.
Generally, in a case where a gamma correction is made, as shown in FIG. 26, a gamma correction circuit 131 for making the relationship between the input signal (video signal) and luminance conform to the gamma characteristic is provided on the input side of a display element driver circuit 132. The signal that has been gamma-corrected by the gamma correction circuit 131 is input to the display element driver circuit 132, and the data signal is supplied from the display element driver circuit 132 to a display element panel 133 via a data signal line. Since the gamma correction circuit 131 is necessary in this arrangement, however, not only is the circuitry large in size but an additional problem is a reduction of grayscales that can be expressed. For example, if the gamma characteristic (gamma value=2.2) is expressed using an 8-bit (256 grayscales) display element driver circuit 132, only 187 grayscales can be realized.
In order to implement a gamma correction having grayscale (256 grayscales) the same as those of the input signal, on the other hand, it is necessary that the gamma correction circuit 131 and display element driver circuit 132 be capable of supporting more grayscales than those of the input signal, as illustrated in FIG. 27. Consequently, the circuitry is large in size. In the example illustrating in FIG. 27, both the gamma correction circuit 131 and display element driver circuit 132 support 512 grayscales (nine bits).
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-2-148687, pages 5 and 6, FIG. 2)
Thus, in a case where the conventional display circuit is provided with a gamma correction function, a problem which arises is the large size of the circuitry, as mentioned above. The same is true also in a case where a gamma correction of grayscales identical with those of the input signal is performed.